Nitrogen Applications for Select Asian Vegetables

Wells, B., DPM, Extension Agent II, UF/IFAS Extension St. Johns County, St. Augustine, Florida, 32092, and G. Liu, Ph.D., Assistant Professor, University of Florida, Gainesville, Florida, 32611

Situation: Asian vegetable acreage is increasing in Florida as growers seek alternative crops to stay competitive. However, optimal fertilizer applications to increase grower returns and minimize environmental impacts have not been established for these crops. Objectives: This project aims to determine optimal nitrogen (N) rates for selected Asian vegetables by evaluating the effect of N rates on crop yield and petiole nitrate levels. Methods: Field trials were established in Hastings, Florida on July 29, 2015, using bitter melon (Momordica charantia L.), yardlong bean, (Vigna unguiculata subs. sesquipedalis), and luffa (Luffa cylindrica (L.) Roem). Fertigation through drip irrigation was used to apply N rates of 50, 100, and 150 lbs per acre using an 8-0-8 liquid fertilizer to the plantings that were randomly assigned with 4 replications. Petiole nitrate levels were determined using a HORIBA LAQUA Twin nitrate meter (Model: B-741), with sap measured at flowering, early fruiting, and late fruiting. Fruit number and weight were measured at 50-89 days after planting. Results: Petiole nitrate levels and yields were highest with 150 lb/ac N and lowest with 50 lb/ac N; however, significant yield increases were only seen with bitter melon. Luffa had a similar yield tendency but with more mixed results. Yardlong bean is an effective nitrogen fixer and did not have much difference in yields. Conclusions: Field evaluations will be repeated with improvements in 2016. Data collected from these trials will ultimately aide Asian vegetable growers in making efficient fertilizer application decisions thereby maximizing profits and minimizing environmental impacts.